Soil organic carbon (SOC) is a principal regulator of soil fertility and one of the largest terrestrial carbon pools. This popular article reviews how 'ancient' seeds (traditional landraces and locally adapted varieties) and modern hybrid seeds influence SOC through differences in root architecture, biomass allocation, phenology and management practices. Evidence indicates that genotype-driven differences particularly root biomass and rhizosphere interactions can alter carbon inputs to soil (Heinemann et al., 2023; Junaidi et al., 2018). However, effects of seed type cannot be divorced from cropping systems, management (tillage, residue return, fertilization) and environment, which which Paustian et al. (1997, 2016) and Sanderman et al. (2010) identify as the primary controls on SOC. The article synthesizes empirical studies and outlines research and policy implications for breeding and carbon-smart agriculture.